This section provides background information related to the present disclosure which is not necessarily prior art.
Portable devices such as mobile phones and mobile computers may incorporate light guide plates for ten-key illumination, displays, and various types of indicators. These portable devices may be required to be thinner and to be more complicated in shape. The light guide plates may similarly be required to be flexible corresponding to portable devices which are made thinner and complicated in shape.
As a conventional light guide plate, molding of hard acrylic resin or polycarbonate has generally been used. Additionally, in order that light that has entered from a side surface of a light guide plate exits from the front surface of the plate, a minute concave and convex pattern has generally been made on the front surface when molded. FIG. 3 shows an example of the configuration of a conventional light guide plate and peripheral members of the plate. FIG. 3(A) shows the light guide plate and the peripheral members as viewed from a side surface parallel to the entering light. FIG. 3(B) shows the convention light guide plate and peripheral members of the plate viewed from a side perpendicular to the entering light. As shown in FIG. 3, formed on the rear surface of the conventional light guide plate 21 is a rear surface emission prism 21a. Additionally, formed on the front surface of the light guide plate 21 is a front surface emission prism 21b. 
When light from an LED module 25 enters into the side surface of the light guide plate 21, as shown in FIG. 3(A), a part of the light that has entered into the light guide plate 21 is reflected internally by the rear surface emission prism 21a, refracted by the front surface emission prism 21b of the light guide plate 21, and then exits toward a prism sheet 24. In addition, light that has exited toward the rear surface of the light guide plate 21 from the rear surface emission prism 21b is reflected by a reflecting sheet 27 and enters into the light guide plate 21 again, and finally exits toward the prism sheet 24. The direction of light that has exited toward the prism sheet 24 from the light guide plate 21 is adjusted by prisms of the prism sheet 24 and exits from the opposite surface of the prism sheet 24. Such a conventional light guide plate is formed by molding, and thus has a limit in reduction of thickness. Furthermore, when such a conventional light guide plate of a material such as hard acrylic resin or polycarbonate is made thinner, the light guide plate does not have enough mechanical strength and thus is easily damaged disadvantageously.
To address this, a polycarbonate film or a PET film has been used as the material for a thinner light guide plate. When a resin film is used as the material for the light guide plate, however, it is difficult to form a concave and convex pattern by molding. Therefore, a reflecting or scattering pattern is formed on the rear surface of the light guide plate by means of printing or coating, whereby light propagating within the light guide plate exits from the front surface of the light guide plate.
Generally, such a reflecting or scattering pattern is formed by spraying a coating material containing a pigment over the rear surface of the light guide plate, or printing the pattern by screen-printing. However, such a method requires the formation of a mask in advance, leading to high consumption of cost and time disadvantageously. The spraying method is inconvenient because it is difficult to make the thickness of the pattern evenly and hence leading to poor reproducibility of the pattern. The screen-printing method is also inconvenient because it is difficult to form a thin film and hence to control the thickness of the film and its shape in cross-section.
Besides the foregoing techniques, there has been an attempt to form a dot pattern by printing resin into a lens shape by ink-jetting (see, for example, Patent Document 1). It is supposed that a dot pattern can be formed in a mirror hemispherical shape due to the surface tension of the resin with this technique.
However, with the techniques of applying/printing ink or resin to/on the base material of a film-like light guide plate to form a pattern, the ink or resin once cured has no flexibility. This leads to a risk of damaging or peeling of an ink or resin layer when the film-like base material deforms. Therefore, it has been difficult to form a pattern on a flexible elastomer film.    Patent Document 1: Japanese Patent Application Laid-Open No. 2005-249882